I took the basic design from my GPS clock board and replaced the GPS module and its infrastructure with a mini-DIN-6 jack to pull the GPS NMEA sentences and PPS from the GPSDO output. When I tried this with the xCXO variant, there was some impact on the output stability, but I had a brainstorm today... The FE-5660A's output stability shouldn't be impacted at all by the 5 volt supply on the discipline board. The new prototype of the FE discipline board has the new mini-DIN 6 diagnostic jack, of course, so it can power and provide data for the clock board easily enough.

The result is quite nice. It's the same as the existing GPS clock, but as an accessory for the FE GPSDO instead of a standalone device.

I think it's a keeper. :)